The present invention relates to the field of surgical apparatus, and, more particularly, to tissue dilation.
Dilation of tissue is important for many surgical procedures, including vessel harvesting. Tissue must be dilated to allow atraumatic advancement of surgical instruments within the body to a surgical site. For example, to perform a vessel harvesting procedure, a ligation tool, typically maintained within a cannula providing endoscopic visualization, must be advanced to a vessel of interest to ligate the ends of the vessel and any intermediate side branches. However, prior to advancing the ligation tool, the path to the vessel end must be created while creating as little trauma to the surrounding tissue as possible. Many of the present systems used in endoscopic vessel harvesting incorporate a transparent tapered tip to dissect the vein from surrounding connective tissue, and then dilate the peri-vascular cavity by serially inflating a short balloon along the length of the cavity. Mechanical means of dilating the cavity have also been described, for example, such as those described in U.S. Patent No. 6,030,406, including moving arms or cams which expand outward upon activation of a sleeve or a trigger. In these embodiments, a balloon or active mechanical dilator of short length is used, because the short length ensures that the dilators will be able to generate an adequate amount of force to successfully dilate the tunnel. For example, it is known that a short angioplasty balloon generates greater dilating force than a long angioplasty balloon. The wall tension of an inflated balloon is responsible for generating the dilating force. The longitudinal wall of a long balloon maintains less tension in the middle area of the balloon. This area of less tension corresponds to a diminished dilating force. Thus, many surgeons prefer using short balloons because a short balloon can maintain tension across the entire body. However, a short balloon or mechanical dilator in a tissue-dilating system must be activated multiple times along the length of the tunnel to achieve a complete expansion of the tunnel. This repeated motion may tire the hand of a surgeon performing the procedure, and, further, stepwise dilation may result in formation of an uneven tunnel, with an irregular inner contour. Therefore, an apparatus and method are needed that provide adequate tissue-dilating force, result in an even dilation, and do not require multiple repeated movements to complete the dilation procedure.
Apparatus and method according to the present invention perform uniform dilation of tissue while avoiding repetitive actuations and high level forces applied by the user. In a preferred embodiment, a tissue expanding device is pulled longitudinally along an expansible sheath to dilate an extravascular tunnel. In one embodiment, the tissue expansion device is positioned immediately proximal to a transparent tapered tip of a cannula and is formed as a wedge or olive. The distal end of the expansible sheath is compressed against the outer surface of the cannula by a resilient connector, and, in one embodiment, the expansible sheath ends in a solid sleeve proximally. Then, as the tissue expansion device is retracted through the expansible sheath, the resilient connector expands outwardly to permit the tissue expansion device to be retracted into the expansible sheath. As the tissue expansion device is moved toward the proximal end of the cannula through the expansible sheath, the sheath expands concurrently with it, providing an even dilation of the surrounding tissue. The tissue dilation may be obtained through one smooth motion of pulling back on the inner cannula, thus avoiding repetitive motions. The sheath is preferably made of a rigid or semi-rigid material and the tissue expansion device has an enlarged maximal dimension. The force exerted on surrounding tissue by the expansion of the sheath as a result of the movement of the tissue expansion device within the sheath is therefore sufficiently high to provide adequate dilation of the surrounding tissue.
An alternate tissue expansion device may incorporate an expansible sheath that ends in a solid transparent tapered cone distally and a solid sleeve proximally. Adjacent to the proximal solid sleeve is a sheath of an enlarged diameter that houses a wedge or olive that slides along the cannula to expand the expansible sleeve. In this embodiment, the tissue expansion device is pushed along the cannula within the expansible sheath using a push rod that extends in a proximal direction from its attachment point to the olive. As the tissue expansion device is pushed through the sheath, the sheath expands and dilates the surrounding tissue.
A method for performing a vessel harvesting operation in accordance with the present invention includes incising the skin overlying a vessel of interest, bluntly dissecting the tissue overlying the vessel, advancing the cannula to the end of the vessel under endoscopic visualization, retracting the tissue expansion device longitudinally toward the proximal end of the device or pushing the tissue expansion device toward the distal end of the device, and thus concurrently dilating the tissue around the vessel, extending the tissue expansion device to its original distal position to contract the sheath for additional dilation, and then removing the cannula from the body. Thereafter, additional instruments may be inserted into the dilated tunnel to perform the required surgical operations.